The invention relates to a method for measuring the distance to at least one target. Such methods are used in particular in distance-measuring devices as used, for example, in the surveying of buildings and lots.
DE-A-41 33 196 discloses a method of the generic type in which an input signal is composed of signals which are attributable to a plurality of optical pulses which are reflected by a target whose distance is to be determined and which, in order to improve the time resolution, were each emitted with different internal delays. From the time when said input signal reaches its maximum, the transit time is then derived and the distance is calculated therefrom.
This method has the disadvantage that the determination of the distance is based in the end on an individual measured value or at best on a small number of measured values. If these individual or few measured values are falsified by noise, which cannot be ruled out, the result may likewise contain a large error.
Although DE-A-36 20 226 discloses that the noise of the input signal can be reduced by repeated emission of the pulse and addition of those scanned values of the received signal which correspond to the same transit times, this requires a large number of pulses and hence longer measuring times, in particular if a high resolution is also to be achieved.
It is the object of the invention to provide a method of the generic type in which the relationship between the achievable accuracy and the required effort, in particular the number of pulses required and hence the measuring time required, is improved, and high accuracy of the distance measurement is achieved in particular with a small number of pulses or even with a single pulse.
The invention provides a method in which the total shape of the input signal is used for the determination of the transit time. This greatly reduces the dependence of the result on any individual scans falsified by noise. The distance can be determined with great accuracy and low uncertainty of measurement simply from the evaluation of the input signal resulting from a single optical pulse. Moreover, it is readily possible with the method according to the invention to detect and to distinguish a plurality of targets with a single measurement. This is important especially in the case of long measuring distances where, owing to the widening of the beam, the latter need no longer be concentrated on a single target.